Manufacturing of a thin film, transistor (TFT), a color filter (CF), and the like to be used in, for example, a semiconductor device such as an LSI and a VLSI or a liquid crystal display device (LCD) includes a photolithography step using an exposing device. In this step, dust preventing means called a pellicle is generally used.
The pellicle is generally obtained by bonding on one surface of a support frame formed of an aluminum material having a shape corresponding to that of a photomask or a reticle and having a thickness of about several millimeters a transparent polymer film (optical thin film) having a thickness of about 10 μm made of nitrocellulose, a cellulose derivative; a fluorine polymer, or the like, while expanding the film. The pellicle prevents foreign materials from directly adhering onto the photomask or the reticle. In addition, even when foreign materials adhere onto the pellicle, such foreign materials do not form images on, for example, a wafer onto which a photoresist has been applied. Therefore, it is possible to prevent short circuit, disconnection, and the like of an exposure pattern due to images from the foreign materials, and improve a manufacturing yield in the photolithography step.
In manufacturing of the support frame for a pellicle, an aluminum material is generally blackened after anodic oxidation treatment for the purposes of, for example, preventing reflection of light from a light source to provide a clear transferred image of a pattern and facilitating a foreign material adhesion test before use. For example, there have been known a blackening method involving impregnating pores of an anodic oxide film with an organic dye or the like (for example, see Patent Literature 1) and a blackening method involving electrolytic deposition of Ni, Co, or the like into pores of an anodic oxide film (for example, see Patent Literature 2).
Meanwhile, in recent years, along with high integration of a semiconductor device or the like, a circuit pattern has been required to be drawn more finely with a lower line width and mainstream exposure light to be used in the photolithography step has been a short-wavelength light such as a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), a F2 excimer laser (wavelength: 157 nm), or the like. A light exposure source for such short-wavelength light has a high output power and high light energy. When the support frame is irradiated with such high-energy light, the organic dye may be chemically altered to cause a change in color tone or color fading when the anodic oxide film is blackened with the organic dye as described above.
In addition, in the case of blackening through electrolytic deposition treatment, solution control including pH and solution temperature control is generally important, the electrolytic deposition treatment has high facility cost, and equipment for treating waste liquid is required. For such reasons, a method of manufacturing a support frame for a pellicle by a simpler step has been demanded. Besides, there may arise the following problem: an A7075 aluminum alloy specified by JIS is generally used for the support frame for a pellicle because an optical thin film is bonded thereonto while being extended and such state is required to be maintained with high accuracy, but when an Al—Zn—Mg based aluminum alloy such as JIS A7075 is subjected to anodic oxidation treatment and then to electrolytic deposition treatment as described in Patent Literature 2, the aluminum alloy is not sufficiently blackened.
On the other hand, in the case of anodic oxidation treatment using a sulfuric acid solution, there arises the following additional problem: an inorganic acid such as sulfuric acid or phosphoric acid remains in the anodic oxide film on the surface of the aluminum material owing to the acid solution, such inorganic acid reacts with a basic substance such as ammonia present in an exposure atmosphere to generate a reaction product such as ammonium sulfate, and the reaction product (haze) causes fogging in the pellicle and affects a transferred image of a pattern.